You're no more active as a teenager than you will be at 60, according to a new study

Teenagers may be no more active than 60 year olds.Jeremy Thomas / UnsplashIt's a common belief that youthfulness is synonymous with being active.

However, while this may well be true when comparing young children to pensioners, the level of physical activity people take part in isn't as much of a gradual downward slope over the years as you might think.

The researchers used data from the National Health and Nutrition Examination Survey from 2003-2004 and 2005-2006, totalling 12,529 participants altogether. Subjects wore tracking devices for seven days straight, removing them only for washing and sleeping, which measured how much time they were sedentary or exercising. The exercise categories were divided into light or moderate to vigorous physical activity.

Participants were grouped into five age groups: children aged six to 11, teens aged 12 to 19, young adults aged 20 to 29, midlife adults aged 31 to 29, and older adults aged 60 to 84. 49% of them were male, and the rest female.

The study found that during childhood and adolescence, physical activity lowered sharply by age until age 19, where the levels are similar to that of 60 year olds. After age 20, however, physical activity starts increasing by age until midlife, where a gradual decline began again.

Activity among the 20-somethings was spread out throughout the day, with an increase in physical activity in the early morning, compared to younger adolescents. The researchers note that this could be related to a number of things including starting full-time work, having more responsibilities around the house, or becoming a parent.

"Activity levels at the end of adolescence were alarmingly low," Vadim Zipunnikov, assistant professor in the Bloomberg School's Department of Biostatistics and senior author of the study, said in a statement. "For school-age children, the primary window for activity was the afternoon between 2 p.m. and 6 p.m. So the big question is how do we modify daily schedules, in schools for example, to be more conducive to increasing physical activity?"

There were differences shown between males and females, too. Men generally had higher levels of physical activity during their teenage years and early adulthood, but the levels dropped more sharply than in women from midlife to older adulthood. In the 60+ group, men were sitting down more than women and did less light-intensity exercise. Overall, females aged over 31 were increasingly more active than males after 12 p.m.

The researchers note that the majority of studies suggest that males are more active than females at older ages, but a few have shown a reversal of this, including this new research. They say this is potentially because women tend to do a lot more indoor activity than men, such as housework, but the reasons cannot be certain.

Most strikingly, the study showed that World Health Organization recommendations of daily physical activity probably aren't being met. The WHO states children up to age 17 should be getting 60 minutes of moderate-to-vigorous physical activity per day. A quarter of boys and half of girls aged six to 11 hadn't met this target, and neither had half of male and 75% of female teens aged 12 to 19.

"The goal of campaigns aimed at increasing physical activity has focused on increasing higher-intensity exercise," says Zipunnikov. "Our study suggests that these efforts should consider time of day and also focus on increasing lower-intensity physical activity and reducing inactivity."